Concrete in Australia Vol 39 No 1 53
concrete prisms containing particular hazardous waste were
placed in a Soxhlet Extractor, as shown in Figure 1. e flask
at the bottom of the extractor was heated; the water vapour
condensed in the cooling section at the top and distilled water
then gradually filled the middle section. As the water level
reached the siphon, it drained into the bottom flask. Any
potentially soluble material was deposited in the flask, thus
representing the extent of chemical weathering of concrete,
subjected to the cycles of wetting and drying (Samarin, 1979).
After many hundreds of cycles, representing exposure of
concrete to tropical rain with the subsequent drying, the
water in the flask was chemically analysed in order to detect
traces of hazardous material, which had the potential of being
leached from the concrete. When concrete was produced in
accordance with the theoretical and practical methodology,
as described above, even after many hundreds of cycles, only
negligible amounts, in effect only traces of hazardous material
were detected. Even so, for the additional safety of disposal, it
was proposed to incorporate this concrete into a base of special
highway pavements (Samarin, 1997).
3.0 NEW CONCEPT OF PAVEMENT
CONSTRUCTION INCORPORATING
WASTE DISPOSAL
An interesting historical heritage that provides us with the
evidence of extreme endurance, of practically maintenance-
free performance of pavements, is the method used
RAINFALL
ELUVIATE
DRAINAGE
LESSIVATE
ZONE OF
WATER -- TABLE
FLUCTUATION
ATMOSPHERIC
ZONE
CONCRETE OR
MORTAR SPECIMEN
IN A PAPER THIMBLE
Figure 1. Soxhlet Extractor adopted for weathering test.
in construction of the ancient Roman roads. Romans
implemented three basic methods of road construction. In
the countryside, where only minor movements of military
and civilians were expected via terrena -- a plain road was
formed simply by levelling the earth surface. In the areas of
more intense and important traffic, via glareata -- a roadway
surfaced with gravel provided a more reliable thoroughfare.
But the pinnacle of Roman ingenuity was via munita -- a
complex and enduring construction (Vitruvius, 1960).
Of these, the Appian Way -- Via Appia, completed in 312
BC, was considered "the queen of the long roads". Its total
length was some 560 km, connecting Italy s southeast coast with
Rome. During the Second World War, the Appian Way served
as a reliable thoroughfare for the advancement of the allied
troops towards Rome.
e riding surface of this pavement was formed in stones,
which were cut in such a way that they fitted tightly. e sub-
base contained broken stones or pebbles, which were cemented
together with mortar, consisting of sand and yet another
ingenious Roman invention -- hydraulic cement. is cement,
as described by Vitruvius, was composed of lime and volcanic
ash, an invention, the knowledge of which was lost in Europe in
the Middle Ages, and rediscovered only as a Portland cement,
which was patented by John Aspdin in 1824.
But the concept taken from via munita, which I am
proposing to incorporate into the modern pavement, is its base,
which in via munita consisted of broken stones placed on the
bottom of the trench, and upon which the entire roadway was
then erected.
If, when constructing major interstate highways, a "raft
foundation" containing special concrete in which hazardous
wastes are encapsulated is formed, then the two major problems
facing safe vehicular travel and safe waste disposal can be
effectively and efficiently solved.
As most of the road surface pavement failures (cracking,
subsidence and pot-holes) are the result of increased plasticity or
even liquefaction of the base, which is then unable to support
the top layers, a "raft foundation should successfully prevent
this from happening.
Incorporation of hazardous wastes into the "raft foundation"
made with special concrete, as described above, should provide
additional safety from their potential environmental impact.
Obviously, the price of this construction is expected to be
somewhat higher than the existing methods of highway design,
but if the cost of the current methods of hazardous wastes
disposal becomes an integral part of a road construction,
I believe that not only the total expenditure will be less or
comparable, but the enormous savings in the long term
maintenance, in the avoidance of accidents, which often lead to
the injuries and even death of road users, can more than justify
this method of "construction-disposal" of our highways.
I would also like to mention that the cost of ingredients of the
proposed highly durable concrete should be comparable or even
less, than the cost of constituents in most of the conventional
high strength concretes.
4.0 CONCLUSION
e combined method of highway construction and